Durham University - Mathematical Sciences
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Fri, 05 Oct 2018 14:03:15 +0100Andreas Kyprianou: Entrance and exit at infinity for stable jump diffusions (2018-10-17 13:30:00)This talk is part of the afternoon workshop "Random Processes and Heavy-tailed Phenomena". See the website http://community.dur.ac.uk/nicholas.georgiou/htp.html for the talk abstracts and further information about the workshop. (All are welcome: it is not necessary to register in order to attend the talks only.)https://www.dur.ac.uk/mathematical.sciences/events/seminars/?id=5625&seminar=5625
https://www.dur.ac.uk/mathematical.sciences/events/seminars/?id=5625&seminar=5625
Fri, 05 Oct 2018 14:03:15 +0100Bernard Piette: Software on the maths Linux computers (2018-10-17 14:00:00)In the talk I will list and briefly describe a list of useful applications available on the Linux computers in maths. The lists extends from tools to manipulate pdf files to mathematical packages like mathematica or maxima.https://www.dur.ac.uk/mathematical.sciences/events/seminars/?id=5466&seminar=5466
https://www.dur.ac.uk/mathematical.sciences/events/seminars/?id=5466&seminar=5466
Mon, 15 Oct 2018 11:22:55 +0100Nadia Sidorova: Heavy tails and the parabolic Anderson model (2018-10-17 14:20:00)This talk is part of the afternoon workshop "Random Processes and Heavy-tailed Phenomena". See the website http://community.dur.ac.uk/nicholas.georgiou/htp.html for the talk abstracts and further information about the workshop. (All are welcome: it is not necessary to register in order to attend the talks only.)https://www.dur.ac.uk/mathematical.sciences/events/seminars/?id=5626&seminar=5626
https://www.dur.ac.uk/mathematical.sciences/events/seminars/?id=5626&seminar=5626
Fri, 05 Oct 2018 14:01:46 +0100Nicholas Georgiou: A Lamperti problem for heavy-tailed random walks (2018-10-17 15:40:00)This talk is part of the afternoon workshop "Random Processes and Heavy-tailed Phenomena". See the website http://community.dur.ac.uk/nicholas.georgiou/htp.html for the talk abstracts and further information about the workshop. (All are welcome: it is not necessary to register in order to attend the talks only.)https://www.dur.ac.uk/mathematical.sciences/events/seminars/?id=5627&seminar=5627
https://www.dur.ac.uk/mathematical.sciences/events/seminars/?id=5627&seminar=5627
Fri, 05 Oct 2018 14:02:47 +0100Carlo Collari: Slice-torus link invariants (2018-10-18 13:00:00)With the advent of knot homology theories such as Khovanov and knot
Floer homologies, new invariants to study knot concordance have been
developed. For example, Rasmussen's s-invariant, the Ozsvath-Szabo tau-invariant and the s_N invariants due to Lobb and Wu, independently, and another family of invariants introduced by Lewark and Lobb.
All these invariants share three fundamental properties, which were identified by Livingston, and were called ''slice-torus invariants'' by Lewark.
Some among the slice-torus invariants, namely s, tau and the s_N's admit a generalisation to strong concordance invariants for links. Motivated by the properties shared by these extensions, together with A. Cavallo, I gave the definition of slice-torus link invariants and studied their properties.
In this seminar I will give the definition of slice-torus link
invariants, and describe some of their properties. Finally, I will
give some applications and define some new strong concordance invariants
using Whitehead doubling. https://www.dur.ac.uk/mathematical.sciences/events/seminars/?id=5693&seminar=5693
https://www.dur.ac.uk/mathematical.sciences/events/seminars/?id=5693&seminar=5693
Tue, 11 Sep 2018 18:51:51 +0100Ă–mer Gurdogan: Cluster Adjacency and the NMHV 7-particle amplitude in N=4 super Yang-Mills at 4 loops (2018-10-19 13:00:00)The idea of constructing scattering amplitudes from their
singularities has been a very powerful method for their computation. We
introduce the principle of Cluster Adjacency, which governs the analytic
structure of amplitudes at tree and loop level. We use this to compute the
NMHV scattering amplitude of seven particles in N=4 super Yang-Mills at
four loops.https://www.dur.ac.uk/mathematical.sciences/events/seminars/?id=5722&seminar=5722
https://www.dur.ac.uk/mathematical.sciences/events/seminars/?id=5722&seminar=5722
Tue, 25 Sep 2018 10:46:50 +0100Roger Scott: Magnetic Structures at the Boundary of the Closed Corona (2018-10-19 15:00:00)The topology of coronal magnetic fields near the open-closed magnetic flux boundary is important to the the process of interchange reconnection, whereby plasma is exchanged between open and closed flux domains. Maps of the magnetic squashing factor in coronal field models reveal the presence of the Separatrix-Web (S-Web), a network of separatrix surfaces and quasi-separatrix layers, along which interchange reconnection is highly likely. Under certain configurations, interchange reconnection within the S-Web could potentially release coronal material from the closed magnetic field regions to high-latitude regions far from the heliospheric current sheet where it is observed as slow solar wind. It has also been suggested that transport along the S-Web may be a possible cause for the observed large longitudinal spreads of some impulsive, 3He-rich solar energetic particle events. Here we demonstrate that certain features of the S-Web reveal structural aspects of the underlying magnetic field, specifically regarding the arcing bands of highly squashed magnetic flux observed at the outer boundary of global magnetic field models. In order for these S-Web arcs to terminate or intersect away from the helmet streamer apex, there must be a null spine line that maps a finite segment of the photospheric open-closed boundary up to a singular point in the open flux domain. We propose that this association between null spine lines and arc termination points may be used to identify locations in the heliosphere that are preferential for the appearance of solar energetic particles and plasma from the closed corona, with characteristics that may inform our understanding of interchange reconnection and the acceleration of the slow solar wind.https://www.dur.ac.uk/mathematical.sciences/events/seminars/?id=5753&seminar=5753
https://www.dur.ac.uk/mathematical.sciences/events/seminars/?id=5753&seminar=5753
Thu, 11 Oct 2018 14:36:21 +0100Du Haliang: (2018-10-22 12:00:00)https://www.dur.ac.uk/mathematical.sciences/events/seminars/?id=5697&seminar=5697
https://www.dur.ac.uk/mathematical.sciences/events/seminars/?id=5697&seminar=5697
Thu, 06 Sep 2018 13:43:44 +0100Tom Bridgeland: Stokes data and wall-crossing (2018-10-22 16:00:00)There is a very suggestive analogy between the Kontsevich-Soibelman wall-crossing formula for Donaldson-Thomas invariants, and the notion of an iso-Stokes deformation in the theory of differential equations. I will try to explain this analogy in elementary terms assuming no previous knowledge of either of these topics. I'll start by talking about how the Stokes matrices of a differential equation are defined in a simple example, then switch to quiver representations and talk about Donaldson-Thomas invariants and the wall-crossing formula. If there's time at the end (which there probably won't be) I'll talk a bit about some of the recent research which this analogy has inspired.https://www.dur.ac.uk/mathematical.sciences/events/seminars/?id=5315&seminar=5315
https://www.dur.ac.uk/mathematical.sciences/events/seminars/?id=5315&seminar=5315
Tue, 16 Oct 2018 12:00:41 +0100Sam Chow: Ramsey-theoretic properties of diagonal equations (2018-10-23 14:00:00)Arithmetic Ramsey theory is about large sets necessarily containing given structures, such as arithmetic progressions. These phenomena can be studied using combinatorics, analysis, or ergodic theory. For this reason, Szemeredi's theorem has been described as a Rosetta stone of mathematics. The theory for linear patterns is classical, but over the past two years we've been able to Fourier-analytically transfer the results to higher-degree diophantine equations. This has led to a complete characterisation of density and partition regularity for diagonal equations in sufficiently many variables. This talk is based in part on joint work with Sofia Lindqvist and Sean Prendiville.https://www.dur.ac.uk/mathematical.sciences/events/seminars/?id=5717&seminar=5717
https://www.dur.ac.uk/mathematical.sciences/events/seminars/?id=5717&seminar=5717
Sat, 13 Oct 2018 17:16:31 +0100